This is is the IP address of ppa.launchpad.net. I guess this is currently blocked on your network.

You could also try certbot-auto, which does not use distribution package managers. It ultimately downloads the packages from the Python package distribution system PyPi, which uses a different set of servers.

Our instructions for obtaining certbot-auto suggest running

wget https://dl.eff.org/certbot-auto
chmod a+x certbot-auto

(If you do get a certificate error when trying to download by this method, please don’t override it because we rely on the HTTPS connection to ensure the integrity of the software download.)

certbot - Certbot is EFF's tool to obtain certs from Let's Encrypt and (optionally) auto-enable HTTPS on your server. It can also act as a client for any other CA that uses the ACME protocol.

This is not a recommended method because (1) you have to get the software dependencies yourself, (2) you have to set up the Python virtual environment yourself, and (3) it doesn’t update automatically to newer versions. However, it might be a possible method for you if other methods don’t work.

Finally, Certbot is only one of many Let’s Encrypt client applications, so if you can’t get it, you could also try a different one:

Last updated: May 25, 2018 | See all Documentation
Let’s Encrypt uses the ACME protocol to verify that you control a given domain name and to issue you a certificate. To get a Let’s Encrypt certificate, you’ll need to choose a piece of ACME client...